Ultrasonic Method Of Cleaning

ABSTRACT

A method of cleaning utilising ultrasound to boost bleach performance.

Over the last few years environmental and cost saving pressures have lead the automatic machine cleaning industry to offer new automatic dishwashing and laundry machines that have “Eco” wash profiles.

These eco programs generally entail shorter and much cooler wash cycles than have previously been the case. Standard wash temperatures typically reach 65-70° C. in dishwashers and up to 95° C. in laundry machines.

Contrast this with the new eco cycles, wherein the wash temperatures may reach a max of only 30° C. This drop in wash temperature can provide significant energy savings.

In addition, as a result of the same environmental pressures, the amount of wash water used per wash cycle by modern machines has also steadily declined over the years. New ware washing machines now typically only use around 5 L of water per cycle.

However, these changes have brought challenges for detergent manufacture companies to provide automatic dishwashing (ADW) and laundry detergents that are effective at these new lower cycle temperatures. Current detergent compositions have been optimised to work at much higher temperatures (60-70° C.).

One of the biggest challenges within this whole framework of challenges (others include enzyme performance and surfactant performance) is how to provide effective bleach performance at these new lower wash temperatures.

Typically automatic dishwashing and laundry detergents include a bleach to provide effective stain removal performance. Oxygen based bleaches (not chlorine) are generally favoured for ADW and laundry use. For stability, these are provided in precursor form, For example these include peracid based compounds such as percarbonates. The precursor breaks down in situ to generate the bleach (hydrogen peroxide) in the wash liquor.

To able this reaction to occur at viable wash temperatures both bleach catalysts (usually transition metal) and activators (for example TAED) may be added to the detergent composition. Even with these additives this reaction is not fully effective until the reaction temperature reaches at least about 60° C. and bleach performance drops away significantly even at 50° C. This is due to the decomposition reaction being highly temperature sensitive.

It is the object of the present invention to attempt to solve this problem.

In its broadest scope the invention comprises the use of ultrasound energy to activate a bleach precursor in an aqueous cleaning system, wherein the ultrasound energy is not directly applied to the items to be cleaned.

The aqueous cleaning system may comprise an automatic dishwashing machine or an automatic laundry washing machine.

The aqueous cleaning system may also comprise a small portable device for activating bleach at low temperatures for hand dishwashing, hand laundry cleaning and general household hard surface cleaning.

Preferably the ultrasound is able to activate the bleach precursor at low temperatures.

Specifically, low temperature for the purposes of the present invention means from between 10 and 50° C. More specifically it means from between 20 and 40° C.

Generally the term “ultrasound” or “ultrasonic” applied to sound refers to anything above the frequencies of audible sound, and nominally includes anything over 20,000 Hz. For example the frequencies used for medical diagnostic ultrasound scans may extend to 10 MHz and beyond.

For the purposes of all of the aspects and embodiments of the present invention, ultrasound may refer to any frequency of sound between 18 kHz and 10 MHz, preferably between 19 kH and 5 MHz and most preferably between 20 kHz and 1 MHz. The invention is effective across the whole range of this spectra.

In a second aspect, there is provided an ultrasonic method of cleaning soiled tableware in an automatic dishwashing or laundry machine utilising; a programmed wash cycle selected on the automatic dishwashing machine; a detergent composition comprising a bleach precursor; water; and ultrasonic energy; wherein the ultrasonic energy is not directly applied to the soiled tableware or laundry and wherein the ultrasonic energy is used to activate bleach in the wash liquor.

The use of ultrasound in dishwashing generally is well known. For examples, WO 9306947 discloses an improved dishwasher system. US20070131250 A1 discloses an ultrasound drying mechanism for a dishwasher. U.S. Pat. No. 5,218,980, U.S. Pat. No. 3,854,998 and U.S. Pat. No. 3,709,732 all disclose dishwasher systems that incorporate ultrasound generators to provide cleaning.

A more recent disclosure looking at ultrasonic dishwashing is US2009120474 A1.

Ultrasound methods are generally accepted to work by providing localised heat and cavitation bubbles which provide localised scrubbing effects.

The difference between the use of ultrasound in the prior art and the use of ultrasound in the present invention is in its application. Ultrasound in the prior art has been used to directly treat the surface of the tableware to be cleaned. The soiled tableware sits in a liquid medium and the sound waves are directed at the tableware or laundry.

Ultrasound is used by the present invention to activate a bleach precursor in the wash liquor, the wash liquor is then used as normal within the dishwasher or laundry cleaning machine. I.e. The liquor may be pumped around and sprayed onto the dishes and other tableware or articles of clothing. The ultrasound energy is not used directly on the soiled tableware or laundry.

Without wishing to be bound by theory, the applicants believe that the ultrasound is reducing the energy barrier for the decomposition of the bleach precursor. This allows the formation of the active bleach species at a much lower temperature than would normally be possible. Alternatively the ultrasound may be providing an alternative pathway for the decomposition.

The term bleach refers for a large number of chemicals that remove colour, whiten or disinfect. There are two broad classes of common bleaches. Those that are based on chlorine and those based on oxygen.

For the purposes of the present invention oxygen based bleaches are preferred.

Most oxygen based bleaches are based on hydrogen peroxide. Due to its reactivity, hydrogen peroxide is not normally used directly in detergent compositions. A more stable precursor that can be broken down into hydrogen peroxide when needed is normally used.

Non-limiting examples of common oxygen based bleach precursors include sodium percarbonate, sodium perborate sodium perphosphate, sodium persulphate and urea peroxide.

Other non-limiting examples are organic peracids. These are also traditionally used as bleaches in detergent compositions. Preferred examples include perbenzoic acid and peroxycarboxylic acids especially mono- or diperoxyphthalic acid, 2-octyldiperoxysuccinic acid, diperoxydodecanedicarboxylic acid, diperoxy-azelaic acid, 6-phthalimidoperhexanoic acid (PAP) and imidoperoxycarboxylic acid and the derivatives and salts and mixtures thereof.

The bleach precursor may be present between 1 and 50% by weight of the detergent composition, preferably between 5 and 30% by weight and most preferably between 10 and 25% by weight of the detergent composition.

The quantity of detergent composition used per wash cycle may be between 5 and 100 g, preferably 10 and 75 g and most preferably between 15 and 50 g per wash cycle.

The present invention is not limited to particular bleach precursors and may also be used with a combination of two or more different bleach precursors.

The use of ultrasound has been found to boost bleach formation at lower temperatures. The applicants have found significant increases in bleaching power by utilising ultrasound energy on dissolved bleach precursors.

The ultrasonic cleaning method is effective across a range of temperatures. The method disclosed may be effective even when using low temperature “ECO” cycles on newer machines.

The method described may be effective when wash temperatures lower than 50° C. are selected. The method may even be used when wash temperatures lower than 40° C. are selected.

The method described may be effective between 10 and 75° C., more preferably between 20 and 50° C. and most preferably between 30 and 40° C.

The method preferably includes a bleach activator. A preferred bleach activator is tetraacetyl ethylene diamine (TAED).

Other bleach activators that may be included are one or more of an N- or O-Acyl compound, an acylated alkylene diamine, tetra acetyl glycouril, N-acylated hydantoine, hydrazine, triazole, hydratriazine, urazole, di-ketopiperazine, sulfurylamide, cyanurate, a carboxylic acid anhydride, sodium-acetoxy-benzene sulfonate, sodium-benzoyloxy benzene sulfonate (BOBS), sodium-lauroyloxy-benzene sulfonate (LOBS), sodium-isononanoyloxy benzene sulfonate (iso-NOBS), acylated sugar derivatives, pentaglucose, and sodium-nonanoyloxy benzene sulfonate (NOBS) or combinations thereof.

The bleach activator may be present between 0.1 and 5% by weight of the detergent composition.

The method may include the use of a bleach catalyst. Any suitable bleach catalyst may be used for example manganese acetate, manganese oxalate or di-nuclear manganese complexes such as those described in EP-A-1,741,774.

The bleach catalyst may be present between 0.01 and 1% by weight of the detergent composition.

Any detergent composition suitable for use in an automatic or dishwashing machine that comprises a bleach precursor may be used in the present method. Example ADW compositions that may be used in the present invention may be found in WO 2008075084. These are incorporated herein by reference.

The detergent composition comprises one or more of the following additional components, dye, binder, builder, surfactant, preservative, perfume, phosphonate, and/or polymers.

The compositions used are preferably phosphate free.

A suitable commercial example of dishwashing formulations would be the Finish™ brand of dishwasher tablets.

In a third aspect there is provided an automatic dishwasher comprising an ultrasound source, wherein the ultrasound emitter is located such that the ultrasound emitted does not contact the items to be cleaned directly.

Preferably the emitter is located in the water flow system, such that the wash liquor is cycled past the emitter many times during the wash cycle. This also ensures that the ultrasound does not contact the items to be cleaned.

Preferably the emitter will only be activated during low temperature wash cycles.

EXPERIMENTAL

The activation of the bleach precursors by ultrasound was studied the through the IR analysis of the degradation of a dye, Orange II. The precursor and the dye are placed together in a IR cell and the loss of dye colour monitored over time.

The loss of dye colour correlates with activation of the bleach precursor into the active bleach species, as the active bleach quickly degrades the dye.

The results can be seen on the table below:

% Degredation Frequency Temperature Contents of Dye Control - No Ultrasound 40° C. Blank  0% 40° C. PCB/TAED 44% 30° C. PCB/TAED 22% 20° C. PCB/TAED 10%  20 kHz 40° C. Blank N/A 40° C. PCB/TAED 76% 30° C. PCB/TAED 79% 20° C. PCB/TAED 81% 580 kHz 40° C. Blank 11% 40° C. PCB/TAED 78% 30° C. PCB/TAED 39% 20° C. PCB/TAED 21% 864 kHz 40° C. Blank 13% 40° C. PCB/TAED 71% 30° C. PCB/TAED 55% 20° C. PCB/TAED 15%

39 mL of RO water was heated to 5° C. above the experimental temperature. 5 mL of TAED solution (final concentration 0.144 g/L) was added to the water, followed by 1 mL of orange II solution (final concentration 2 ppm) and lastly 5 mL of percarbonate solution (final concentration 0.564 g/L). Either ultrasound or stirring was applied with the reaction temperature held at 40, 30 or 20° C.±1° C.

The samples were taken at 30 minutes and the absorbance measured at 482 nm.

In blank controls: TAED and percarbonate solutions were replaced with 6 mL water and 4 mL sodium carbonate solution (final concentration 0.32 g/L, to adjust pH to >10).

Total volume of each experiment was 50 mL.

The initial pH of TAEDPCB experiments was 10.1-10.4. For blanks (with sodium carbonate added) it was 10.3-10.5.

The power transferred to the experimental system by the ultrasound was determined by way of calorimetric measurements . Two different sources were used for the generation of the ultrasound. The 20 kHz sound was produced by a probe by Sonic & Materials Inc., #VCX600 and the two higher frequencies by a Meinhardt Ultrschalltechnik frequency generator #HM8001-2 in combination with power amplifier #M11-010.

The two devices produced quite different power outputs, the 20 kHz signal provided 21 watts to the experimental system while the higher frequency generator provided a much lower 0.8-1.2 watts to the experimental system.

This may provide the explanation for the marked increase in performance at lower temperatures (20° C.) shown by the 20 kHz signal.

The results clearly demonstrate the activating power of ultrasound at low temperatures making this a highly effective way of boosting cleaning performance in automatic dishwashing under ECO conditions.

The results also show that the ultimate bleaching performance may be controlled through control of the power of the ultrasound used.

Preferably the ultrasonic energy applied to the wash liquor is at least 0.5 watts as measured calorimetrically.

Preferably the ultrasonic energy applied to the wash liquor is in the range between 0.5 to 100 watts, more preferably between 10 and 50 watts and most preferably between 20 and 30 watts as measured calorimetrically.

The power figures above are based on those used in the test bath (˜3.5-4 L).

If the emitter is to be used within a confined space within the device, such as a pipe, with the wash liquor flowing past the emitter many times during the washing procedure for continued activation, much lower energy levels may be required. In this embodiment the ultrasonic energy supplied may be between 1 mW and 1 Watt, preferably between 10 mW and 500 mW and most preferably between 50 mW and 200 mW. 

1. An ultrasonic method of cleaning soiled items in a cleaning machine comprising: preparing a wash liquor from the combination of water with a detergent composition comprising a bleach precursor; selecting a programmed wash cycle on the cleaning machine; contacting the soiled items with the wash liquor during the wash cycle; and applying ultrasonic energy in the cleaning machine; wherein the ultrasonic energy is not directly applied to the items; and wherein the ultrasonic energy is used to activate the bleach precursor in the wash liquor.
 2. The method according to claim 1, wherein the bleach precursor is an oxygen bleach precursor.
 3. The method according to claim 1, wherein the temperature of the wash liquor is less than 50° C. for the entire wash cycle.
 4. The method according to claim 1, wherein the temperature of the wash liquor is less than 45° C. for the entire wash cycle.
 5. The method according to claim 1, wherein the detergent composition further comprises a bleach catalyst.
 6. The method according to claim 1, wherein the detergent composition further comprises a bleach activator.
 7. The method according to claim 1, wherein the detergent composition further comprises one or more components selected from the group consisting of dye, binder, builder, surfactant, preservative, perfume, phosphonate, and polymer.
 8. An automatic dishwashing machine comprising: an ultrasound energy emitter; and a construction such that ultrasound energy emitted from the ultrasound energy emitter cannot encounter the items to be cleaned directly.
 9. The automatic dishwashing machine according to claim 8, wherein the ultrasound energy emitter is located within a water circulation system of the machine.
 10. The use of ultrasound to activate a bleach precursor in an aqueous cleaning system, wherein the ultrasonic energy is not directly applied to the items to be cleaned.
 11. The use according to claim 10 wherein the aqueous cleaning system comprises an automatic dishwashing machine.
 12. The use according to claim 10 wherein the aqueous cleaning system comprises an automatic laundry cleaning machine.
 13. The use according to claim 10 wherein the aqueous cleaning system comprises a portable device suitable for generating activated bleach for hand cleaning of hard surfaces, hand dish washing and hand washing of laundry.
 14. The method according to claim 1, wherein the cleaning machine is an automatic dishwashing machine and the solid items are tableware.
 15. The method according to claim 1, wherein the cleaning machine is an automatic laundry cleaning machine and the solid items are clothes.
 16. The method according to claim 1, wherein the bleach precursor is selected from the group consisting of a percarbonate and sodium percarbonate.
 17. The method according to claim 5, wherein the bleach catalyst comprises manganese oxalate.
 18. The method according to claim 6, wherein the bleach activator comprises TAED. 